The present invention relates to a method for estimation of the quantity of fresh air present in the intake and exhaust manifolds of an internal combustion engine with a recirculation circuit (also known as an xe2x80x9cEGR circuitxe2x80x9d).
As is known, the control system of an internal combustion engine must admit into each cylinder, and as each cycle, a quality of fuel (i.e. petrol or diesel), and a quantity of comburant (i.e. of fresh air containing approximately 20% oxygen), determined such as to make combustion take place in optimum conditions, in order to maximise the performance and reduce the generation of pollutant substances.
In internal combustion engines, the quantity of fresh air which is admitted into each cylinder depends only on the position of the butterfly valve, whereas in internal combustion engines with a recirculation circuit, part of the gases present in the exhaust manifold is recirculated, and admitted into the intake manifold, and thus the quantity of fresh air admitted into each cylinder depends both on the position of the butterfly valve, and on the flow rate and composition of the recirculation gases. In particular, the flow rate of the recirculated gas can reach 30% of the flow rate of the butterfly valve, and the percentage of fresh air in the exhaust gases can reach 50%; it is therefore apparent that up to 15% of the fresh air present in the intake manifold can be obtained from the recirculation pipe.
In order to allow the control system of an internal combustion engine with a recirculation circuit to operate correctly, it is necessary to provide the control system itself in real time with an estimate of the quantity of fresh air present in the intake and exhaust manifolds, so as to allow the control system to actuate both the butterfly valve and the recirculation valve, in order to admit into each cylinder the optimum quantity of fresh air, according to the quantity of fuel provided.
It is know to determine in real time an estimate of the quantity of fresh air present in the intake and exhaust manifolds, by means of a pair of linear oxygen sensors, which are disposed respectively in the intake manifold and in the exhaust manifold; however, this solution is relatively costly, owing to the high cost of the linear oxygen sensors.
It has also been proposed to estimate the quantity of fresh air present in the exhaust manifold, using the signal of the lambda sensor disposed in the exhaust pipe; however, this signal of the lambda sensor which is disposed in the exhaust pipe has delays which are very lengthy (typically of approximately 200 ms) in relation to the duration of a cycle of the engine (variable between 10 and 100 ms), and thus it does not allow the control system to have relatively good dynamic control performance levels (in particular in response to the sudden variations).
The object of the present invention is to provide a method for estimation of the quantity of fresh air present in the intake and exhaust manifolds of an internal combustion engine with a recirculation circuit, which is free from the disadvantages described, and which in particular is easy and economical to actuate.
According to the present invention, a method is provided for estimation of the quantity of fresh air present in the intake and exhaust manifolds of an internal combustion engine with a recirculation circuit.